Hot gas generator utilizing a mono-propellant fuel



United States Patent m 3,533,233 HOT GAS GENERATOR UTILIZING A MON O-PROPELLANT FUEL Willy A. Fiedler, Los Altos Hills, Willi K. Kretschmer, Santa Cruz, and George A. Honzik, Los Altos, Calif, assignors to Lockheed Aircraft Corporation, Burbank,

Calif.

Filed Sept. 13, 1967, Ser. No. 667,482

, Int. Cl. F02g 3/00 US. Cl. 6039.82 2 Claims ABSTRACT OF THE DISCLOSURE The disclosed gas generator utilizes a liquid monopropellant in a two stage ignition system. The fuel in the main chamber is ignited by being impacted by hot gas generated in the pilot chamber. In the pilot chamber the mono-propellant is ignited by an electric heater which works in cooperation with a heat retaining liner.

FIELD OF THE INVENTION This invention relates to improvements in apparatus for igniting and burning a liquid mono-propellant in a combustion chamber.

The igniting and burning apparatus referred to is employed in connection with gas generators, reaction motors, or the like so that the combustion can be terminated or restarted at will. More particularly, this apparatus uses a pilot combustion chamber to ignite a main combustion chamber and utilizes a mono-propellant fuel.

PRIOR ART The starting of prior art reaction motors using a monopropellant was a matter of considerable difficulty because the ignition of the propellant chemical used in such reaction motors generally required additional extra starting energy, called the energy of activation of the chemical system. There are two main liquid propellant reaction systems in general use. One type uses what are known as hypergolic fuels, which are ignited upon contact of the chemicals involved. The other types uses non-hypergolic fuels which are ignited by external energy, i.e., powder trains, spark plugs, fuses, etc. In the former type, fuel must be highly reactive chemically and as a consequence extreme care must be used in its handling. The latter type, which is capable of using such fuels as alcohol, gasoline, kerosene, etc., requires a relatively heavy complex auxiliary starter and is less desirable from the standpoint of simplicity and over-all operation and weight factors.

Another problem with both types of the prior art gas generators was that it was hard, if not impossible, to cycle the production of hot gas. In some prior art systems it was not possible to recycle or restart the gas generator once it had been turned off until the gas generator had completely cooled. Other prior art gas generators were unsatisfactory because of the relatively long time lag between the starting of the reignition cycle and the actual production of hot gas. Moreover, prior art hot gas generators that could be recycled required a large amount of electrical energy for reignition which made them virtually unuseable in situations where electrical energy was not readily obtainable.

An object of the present invention is to provide a system combining the desirable features of systems utilizing non-hypergolic fuels and the simplicity of those systems involving the chemical ignition of hypergolic type fuels The disclosed system uses a liquid mono-propellant composed of a nitrate ester in solution with a densitizing agent and a stabilizer. The characteristics of one useable type mono-propellant is set forth in Safety in Handling In- 3,533,233 Patented Oct. 13, 1970 structions, Otto Fuel II, NavWeps Op 3368, published by direction of the Commander, Naval Ordnance Systems Command, 1966.

A further object is to provide a hot gas generator that is capable of recycling without the necessity of waiting for the device to cool while at the same time having a minimum time lag between the start of the refiring cycle and the actual generation of hot gas.

The present invention can be restarted with a large pulse of propellant without danger of the propellant quenching its own combustion, and if so desired can be sustained at a low flow level giving the device the capability to operate at a wide throttle range.

The present invention utilizes a two-stage ignition system. The first stage consists of a heater in combination with the pilot chamber. The second stage consists of a separate burning chamber in which the main fuel is ignited by the hot gas generated within the pilot chamber.

The foregoing and other features of our invention will be better understood from the following description and accompanying drawing in which:

The figure is a cutaway cross-sectional view of the combustion chamber in combination with the pilot chamber.

DESCRIPTION OF THE. PREFERRED EMBODIMENT Referring to the figure, the reaction motor of the invention is shown to comprise a cylindrical casing 1, having a longitudinal axis. In the arrangement shown, the casing 1 is provided with an integral closure head 2 at the rear end. Casing 1 terminates in the front end in an outwardly flared lip 3. For convenient reference herein, the bottom end of the reaction motor as viewed in the figure is designated the rear end, the top end of the reaction motor as the front end. The integral closure head 2 includes a neck 4 having a generally cylindrical shape to which a nozzle outlet or a hot gas conducting means (not shown) can be attached by any well known means. An end closure piece 5 communicates with and substantially closes the front end of casing 1. A layer of insulation 6 is sandwiched between end closure piece 5 and an annular shoulder 26 formed on the inside face of casing 1 adjacent to the front end. The end closure piece 5 is rigidly attached to casing 3 by any well-known means, such as an annular row of fasteners such as bolt 7, washer 8, and nut 9.

A pilot chamber 10, having a longitudinal axis parallel to the axis of the casing 1, is located within the casing 1. The pilot chamber 10 is a generally hollow cylindrical body having an integral closure head 11 at the rearward end and an annular flange 12 at the front end. The pilot chamber 10 is rigidly affixed to the end closure piece 5 by annular flange 12 by any well-known attaching means, such as illustrated by screw 13.

Within the pilot chamber 10, there is a heater element 14 preferably formed in a cylindrical coil that is supported on its rear end, and insulated from the integral closure 11 by insulative support means 15. Juxtaposed between the wall of pilot chamber 10 and heater 14 is a cylindrical shaped housing 16, the purpose of which will be described hereinafter. The cylindrical shaped housing 16 includes a plurality of elongated radial slots 17 at the rearward end thereof for a purpose that will be described hereinafter. The ends of a heater 14 extend through the insulation 6 and the end closure piece 5 for connection with a source of electrical energy (not shown). These leads extend through plugs 18 which insulate the leads from the end closure piece 5 and also act as a seal to eliminate possible leakage of propellants or gas from the pilot chamber 10. Aperture 19 extends through the end closure piece 5 and includes a swirl injector 20 at the rearward end thereof. Conduit 21 is rigidly afiixed to the end closure piece in a cooperative relationship between aperture 19 and a source of mono-propellant (not shown).

A plurality of fuel delivery apertures 22 form an annular ring around end closure piece 5 and communicate between the annular chamber formed by casing 1 and fuel tube 23. Fuel tube 23 is connected to a source of monopropellant (not shown).

The characteristic length L* of the pilot chamber is critical. If L is too small the performance is decreased and in turn could cause the mono-propellant to quench its own ignition when the temperature of the mono-propellant drops below its burning point, The ideal L* of the pilot chamber can be determined by one of ordinary skill in the art in light of our teaching herein once the characteristics of the particular mono-propellant being used is known and the material to be used in the cylindrical shaped housing 16 is selected.

Due to the configuration of the disclosed gas generator, including the cylindrical shaped housing 16, the characteristic length L* has been reduced from a Value of approximately 600 for the prior art systems to a value of L is defined by the following equation:

L*= where V=Volume of the chamber.

A:Total cross sectional area of the exit apertures of the chamber.

Modifications of this invention described herein will become apparent to those of ordinary skill in the art. For example, although the illustrated embodiment shows an electric heater for heating the mono-propellant, it is understood that a solid propellant or any other well-known high temperature gas source could be used for heating the mono-propellant without deviating from the scope of the invention. Such a modification is possible since the burning of the mono-propellant within the pilot chamber is self sustaining as will be described hereinafter.

METHOD OF OPERATION The mono-propellant flows from the reservoir through tube 21, aperture 19, and swirl injector into the interior of the pilot chamber 10. Electrical energy is supplied to heater 14 so that the mono-propellant is heated to its burning point and thereby ignited. The hot vapor generated by this ignition moves towards the rear end of the pilot chamber 10, through elongated slots 17, into gap 25 and through aperture 24. During this travel, cylindrical shaped housing 16, which is made out of carbon or any other suitable high temperature material having a high heat capacity is heated. Once the pilot chamber has reached quiescent operation, the amount of energy applied to coil 14 can be turned off since the heat energy stored in cylindrical shaped housing 16 is sufficient to sustain the burning of the mono-propellant and overcome the problem of the mono-propellant quenching its own ignition.

When no fuel is being delivered directly to casing 1, the hot gas will exit from the gap 25 through aperture 24 into the space defined by casing 1 and then through the hot gas conducting means attached to neck 4.

When mono-propellant is introduced directly into casing 1 from the source of mono-propellant (not shown) through fuel tubes 23 and aperture 22, the hot gas exiting 4 through aperture 24 impinges upon the mono-propellant and ignites it. The hot gas thus generated exits casing 1 by means of the hot gas conducting means attached to neck 4.

From the above it can be seen that the present invention combines the advantages found in the prior art systems utilizing hypergolic fuels and the prior art systems utilizing non-hypergolic fuels without having the disadvantages of either.

We claim:

1. A gas generator utilizing a liquid mono-propellant comprising I a cylindrical casing having a first and second end, said first end of said casing terminating in a flared lip, said second end terminating in an integral closure head, and end closure piece,

said end closure piece communicating with and substantially closing said first end of said casing,

a pilot chamber mounted within said cylindrical casing,

means in cooperative relationship with said pilot chamber for introducing a first amount of liquid monopropellant into said pilot chamber,

means within said pilot chamber for heating said monopropellant to its burning point, means within said pilot chamber for storing suflicient heat energy to sustain the burning of said mono: propellant within the said pilot chamber once the pilot chamber has reached quiescent operation,

means for venting the hot gas generated in said pilot chamber into said cylindrical casing,

and injection means for introducing a second amount of liquid mono-propellant directly into said cylindrical casing whereby said second amount of liquid mono-propellant introduced directly into said cylindrical casing will be ignited by the said hot gas vented from said pilot chamber.

2. A gas generator in accordance with claim 1 wherein the means for venting the hot gas constitutes at least one passageway extending through the said pilot chamber and connecting the interior of said pilot chamber to the interior of said cylindrical casing, said means for heating said first amount of mono-propellant is a cylindrical electrical coil and said means for storing heat energy is further defined as a cylindrically shaped housing having at least one slot on the end thereof in registry with said passageway, and said cylindrical shaped housing is made of carbon.

References Cited UNITED STATES PATENTS 2,706,887 4/1955 Grow 60-258 2,751,750 6/1956 Welch 6039.46 2,775,866 1/1957 Randall 60-39.46 2,858,672 11/1958 Clark 60-39.46 2,975,588 3/1961 Smith 6039.46 2,981,059 4/1961 Hornet 60257 3,079,755 3/1963 Forney 60-39.46 3,142,541 7/1964 Presbie 60-39.46 3,149,460 9/1964 Rocca 6039.46 3,377,140 4/1968 Hall 60-39.46

MARK M. NEWMAN, Primary Examiner D. HART, Assistant Examiner US. Cl. X.R. 6039.14, 39.46 

